Water storages and rainfall data

Rainfall and dam levels – why does the storage figure sometimes not increase after a big storm?

​This largely depends on soil moisture in the forested catchments that generate most of our drinking water. Catchment soils act like a sponge, so the drier they are the more rain they absorb, leaving less to run off into the dams.

In summer and autumn the ‘sponge’ is typically dry. Summer rain also tends to be patchy, so a one-off shower will only make soils moist before they dry out again, which happens quickly in the heat.

Winter and spring rainfall is more consistent, and once the soils are wet enough more of the following rain will make its way into the dams. The biggest storage gains happen when there are consecutive days and weeks of rain, which typically happens in winter and spring.

Copyright Melbourne Water